Paper manufacture



Patented May 3, 1938 PAPER MANUFACTURE Harold Robert Itafton, Andover,Mass, assignor to Raffold Process Corporation, a corporation ofMassachusetts No Drawing. Application January 21, 1933, Serial No.652,919

12 Claims.

This invention relates to the manufacture of paper. It more particularlyconcerns the manufacture of paper filled with alkaline filler.

The principal object of this invention is to prevent the deteriorationor destruction of the sizing in paper filled with alkaline filler byregulating the temperature to which the web is raised in drying.

An important object is to accomplish this by drying the web on papermachine driers, the surface of said driers having a relatively lowtemperature.

A further object is to prevent this deterioration or destruction bydrying with a heated gas such as air.

A further object is to prevent this deterioration or destruction bymeans of drying in a vacuum.

A further object is to prevent this deterioration Q or destruction byprevention of contact of the paper web with the surface of the steamdrying cylinders.

Other objects and advantages of this invention will become apparentduring the course of the following description.

In the manufacture of paper filled with alkaline filler, as is wellknown, the sizing, for example, size precipitate such as rosin sizepre-' cipitated by alum, is deteriorated in the mix by contact withalkaline filler even to the point of destruction. As is well known fromthe disclosures of my prior patents, this deterioratm'by alkaline filleris not confined to rosin sizing of any definite composition but areaction characteristic of rosin sizings in general. This deteriorationmay be prevented by various techniques suchfor example, as thosedescribed in a number of my already issued patents and copending'applications. For example, it may be substantially prevented byminimizing the time and/or intimacy 40 of contact of the constituents ofthe mix, suitably by adding one or more of the chemically incompatiblematerials at the dilute stage in the papermaking process. It may also besubstantially lessened by lowering the temperature of the paper mix.Likewise, it may be avoided or prevented, for example, by theapplication, precipitation or regeneration of the sizing in the web.Moreover, it may in certain cases be substantially lessened bysuitably-treating the alkaline filler, as with paraffin emulsion, forexample.

Paper is customarily dried on the steam drying cylinders, i. e. driers,of a paper machine and although satisfactory sizing results may-beobtained by my previously described processes when 55 the paper madethereby is thus dried, nevertheless an 'iinyestigation of the effects ofdrying temperaturef giias shown that in many cases the optimum results"from these processes are not obtained at v the temperatures ordinarilyemployed on the 69;; paper machine in drying.

I have found that if the temperature of the wet paper web during dryingis kept at or below a critical temperature, which is approximately 750., much better results are obtained than if higher temperatures areemployed; and apparently the lower the temperature used within certainlimits the better the results.- For example, in certain cases I havefound that a temperature of the web of approximately 65 C. givessubstantially improved results over 75 C. and in many instances atemperature of approximately 45 C. seems to give the optimum sizingeffect.

' I have found that drying at such temperatures I in certain cases notonly gives much better sizing efiect at room temperature, but thiseffect is sub- I stantially enhanced by an increase in temperature ofthe web. Sizing, which for example has been precipitated in the beater,and which, without the employment of minimizing or other specialtechnique, has apparently been deteriorated by the alkaline filler inthe mix even to the point of destruction, in many instances has not beencompletely destroyed before the web contacts with the driers, and thedeterioration reaction is completed at the elevated temperature of thedriers.

By holding the paper web at or below the critical temperature duringdrying, this final action of the alkaline filler on the sizing issubstantially lessened if not in many cases substantially eliminated.

Thus, better sizing is obtained in the case where a sizing efiect wouldotherwise exist, but which might be somewhat deteriorated on the driers,and a moderate degree of sizing is in many instances obtained where nosizing effect would otherwise exist owing to its destruction beingcompleted on the driers. This theory would appear to be substantiated bythe fact that if an alkaline filler paper mix is allowed to remain longenough .and in sufliciently intimate contact actually to complete thedestruction of the sizing before the web is formed, the 'drying at alowered temperature is not effective in producing a sizing efl'ect. Itis only when there is some actual residual effective sizing leftin themix, or when the sizing has been substantially unattacked, or has beenrestored, or produced by the application. of the minimizing or othertechnique, that a sizing eilfect or an enhancement of a sizing effectcan be obtained in the web by the conducting of the drying at or belowthe critical temperature.

As the ordinary paper machines operate with steam drying cylinders atleast some of which are usually above 100 C., it is apparent that it isnecessary to operate such machines somewhat differently in order tocarry out the present invention.

One satisfactory method is to utilize exhaust steam under a considerablevacuum in the driers (i. e. drying cylinders) whereby the surfacetemperature thereof is kept at substantially 75 C. or below. Anothermethod is by passing water or other fluid at suitable temperature,rather than steam, through the driers. Of course it will be apparentthat in either of these cases, a vacuum drier (i. e. a chamber undervacuum in which paper machine driers are enclosed) may be used ratherthan paper machine driers operating in the open air, which will serve tohasten in a marked degree the drying of the paper which is otherwiseslowed down materially by the lower temperatures employed in my process.

I have also found that instead of drying the paper web in contact with asubstantially smooth surface, such as a paper machine drier, whichimparts its heat to the paper by direct contact therewith, if the web bedried by contact with a hot gas such as air, in most cases the sizingeffect obtained is substantially enhanced over that obtained when thepaper is dried by contact with a substantially smooth solid surface.

For example, I have found that although a satisfactorily sized paper maybe obtained by or even higher up to that temperature where' thecellulose would be substantially injured by the heat employed. I havealso found that in many cases when heat is imparted by hot air thehigher the temperature of the air, the better the sizing- I do notbelieve, however, that these findings conflict with my previous findingsrelative to drying in contact with solid surfaces such as paper machinedriers, as the theory which I have evolved relative to hot air dryingharmonizes the two sets of observations.

My theory in this connection is that paper dried in hot air does notreach a substantially higher temperature than, if as high as, the wetbulb temperature corresponding to the relative humidity of the air inwhich it is dried. Thus, even though the paper be dried with air heatedto 75 C. or above, the actual temperature of the web, owing to theabsorption from the web itself of part of the latent heat required inthe evaporation of its water content, is substantially less than thetemperature of the air employed and does not rise as high as or higherthan the critical temperature of 75 C. while any substantial quantity ofmoisture still remains in the paper. Of course it will be understoodthat if air saturated or substantially saturated with moisture isemployed for drying, and said air is at a temperature above 75 0., thetemperature of the web will then rise to substantially the temperatureof the air (but not above 100 C. while it still contains any substantialdegree of moisurated air employed at above 75 C. is not suitable forcarrying out my invention, and hot air should be employed in thecarrying out of my invention only under conditions such that thetemperature of the web is not raised thereby above 75 C., which is onlypossible, if air above 75 C. be used, when such air is not substantiallysaturated with moisture. The theory further postulates that thedestruction of the sizing is a function both of the temperature andtime,

and that the speeding up of the time may so shorten the period duringwhich destruction can take place as to compensate for the greater rateof destruction at the somewhat higher temperature employed providing thetemperature of the paper does not rise too high; and likewise the lowerrate of destruction at a lower temperature may result in actuallygreater sizing destruction by the prolonged time of drying required atthat lower temperature.

Drying at a higher temperature is very much more rapid than drying at alower temperature, and thus when heated air is used for drying, thehigher temperature employed so speeds up the rate of drying thattheincrease in the rate of destruction due to rise in temperature issubstantially counteracted and the net result, may even be a lesseningin the destruction taking place. When using high temperature air fordrying, the temperature of the paper itself is kept reasonably low bythe extremely rapid evaporation of the water with its consequent coolingeffect on the paper itself.

On the other hand, where a contact surface is used for conveying theheat for drying, such as in a steam drying cylinder, the temperature ofthe paper itself is actually raised above the wet bulb temperature whichwould exist at the humidity of the surrounding air, because the water inthe paper itself is directly heated by contact with the drier surface.Thus, paper dried on a drier is in many cases actually heated to thevicinity of the surface temperature of the drier itself, although if thetemperature of the drier is above 100 C., of course, the wet paperitself will not be raised above that point but will approach very closeto it.

It will thus be seen that the drying at a higher temperature on papermachine driers increases the deteriorating effect of alkaline filler onthe sizing for which the lessening time fails to compensate, owing tothe high temperatureto which the paper itself is raisedrwhereas, whenpaper is dried in heated'air out of contact with drying cylinders, thetemperature of'the air, although much higher, than the paper, does notactually raise the temperature of the paper very high and thus theincreased rapidity of drying at the higher temperatures so diminishesthe time that the slight rise, if any, in the actual temperature of thepaper is much more than compensated for, with the result that asatisfactory sizing effect is obtained even at air temperatures up to105 C. and above.

The evidence indicates that the destructive action of the alkalinefiller on the sizing takes place primarily in the presence of asubstantial quantity of water, and that the rate of reaction diminisheswith the reduction in the amount of water or moisture present, becomingsubstantially negligible when most of the water has been eliminated fromthe sheet. It will thus be apparent that in drying, even if the paper atthe end of the drying operation is somewhat raised in temperature,nevertheless the Ii'iB of the temperature of the paper at such time isof little significance because the rate of reaction is then so retarded.

In order to carry out that modification of my invention when the paperis dried by heated air, I may employ for drying the paper a festooningsystem such as is used in certain paper coating machines. This, however,is expensive and also has the disadvantage that the paper with certainfibrous finishes has a tendency to cockle and wrinkle on drying.Therefore, I prefer to dry the paper under tension and for this purposemay provide a chamber in which the paper is passed over a series ofguide rolls, so that it travels under tension in vertical or inhorizontal loops as may bedesired. It has been found that contact withany hot surface has some deteriorating effect on the sizing of the sheetat a high temperature owing to the direct heating of the water in thepaper itself, even though the surface be non-metallic and a relativelypoor conductor of heat such as glass or wood. It is thus better, if itis feasible mechanically, to have the tension rolls over which the paperpasses situated outside of the chamber into which the heated air orother gas is admitted and have the paper pass out of the chamber to thepoints where it passes over these rolls so that the rolls themselves maybe kept substantially cool. Or the rolls if desired may be placed withinthe chamber and be cooled by a suitable fluid such as water.

Ihave disclosed above two means I may employ by which the temperature ofthe web in drying is not raised up to or substantially above thecritical point of 75 C. These means are firstly paper machine driers inwhich the drying cylinder surface temperature is not substantially above75 C., and secondly heated air at any temperature, preferably higherthan 75 C.

There is a third means by which my invention may be carried out, namely,drying on paper machine driers which have a surface temperature above 75C., but under conditions such that the temperature of the web is notraised above 75 C. In this instance means are adopted so that althoughthe surface temperature of the driers is higher than 75 C., the actualtemperature of the web is not raised higher than 75 C., and in manycases is substantially lower.

There are two modifications by which this third means of carrying out myinvention may be practiced. The first modification is by the use of avacuum drier. Mention has been made above of the use of a vacuum dryerwith drying cylinders heated up to 75 C. In the present instance,however. I use drying cylinders heated up to higher temperatures, whichmay be any temperature such as may be employed in drying paper, that is,up to 100 C., and higher if desired. The vacuum drier is then operatedunder a vacuum such that water will boil thereunder at a temperature of75 C. or below, and preferably considerably below 75 C. Under such avacuum the water will evaporate from the web at or below its boilingpoint, and thus the temperature of the web will not rise higher than theboiling point of boils at substantially 33 C., so that regardless of thetemperature of the drying cylinders actually employed, the temperatureof the web will not rise above that point. It should be stated that toobtain well sized paper in a vacuum drier without raising the webtemperature higher than 75 C. is contrary to results previously obtainedin a vacuum drier with rosin sized papers not containing alkalinefiller, where it has been found necessary toheat the still moist web to80 C. or thereabouts in order to obtain satisfactory siz- The secondmodification of my third means is not so eflicient as vacuum drying, butunder certain circumstances is a convenient methodto use. This method isto employ the ordinary paper machine driers and to provide a feltcontacting with the surface of the driers, using in addition if desiredthe ordinary paper machine drier felt. The paper to be dried thuscontacts with the single felt or passes between the two felts and isnever in contact with the surface of the driers.

driers, the temperature of the web can be suitablyregulated. Anotheradaptation of this method is to provide the paper machine driers witlr'aslat surface, such as one made of wood, which will hold the paper awayfrom the surface of the paper machine driers; or to use a textile orother relatively non-conducting jacket for the driers, and thus efiectdrying without substantially contacting the paper with the surface ofthe driers.

As will be apparent, other expedients analogous to these may beutilized, but it should be remembered that the optimum results areobtainable when the web is not contacted at atmospheric pressure abovethe critical temperature with any hot solid object, although wood ortextile surfaces because of their relatively poor heat conductingqualities are better than the surface of paper machine driers and can beused at a higher temperature with better results than can the driers.

As has been stated above, the action of alkaline filler on sizing slowsdown appreciably when the percentage of moisture in the sheet has beenconsiderably lowered and it is thus sometimes feasible to conduct only asubstantial, for instance the major, part of the drying according to themethods disclosed herein. sometimes feasible to use higher dryingtemperatures at atmospheric pressure on those driers which expel thefinal portions of moisture from the paper than on the driers removingthe first portions of the moisture, and thus to speed up the dryingoperation without deteriorating the sizing to any considerable extent,although the web in its latter stages of drying may be raised to atemperature above 75 C.

Where parafiin or other thermoplastic material is used as sizing, or inconjunction with other sizing material, it is in many cases desirable topass the dry or almost dry paper over a drier or driers or the likeheated to at least as high a' temperature as the softening or in somecases:

the melting point of the thermoplastic material in question.

In the prior art the expression "air dried when applied to rosin sizedpapers has meant that the paper has been dried in the air at lowtemperature, i. e. at substantially room temperature. It will beunderstood that the present invention is not concerned with air dryingas thus For example, it is used, but rather with drying with heated air.As a matter of fact, when rosin sized paper filled with alkaline filleris dried in the air at room temperature in certain cases a-moderatedegree of sizing may be obtained, but as explained above, drying withheated air greatly enhances the sizing effect, even up to an airtemperature of 105 C. or higher, and it is to drying with heated airthat this modification of my invention is directed.

The sizing I prefer to employ is rosin size precipitated by a suitableprecipitant such, for example, as alum. Such sizing when usedinsufficient quantity renders the paper substantially water resistant sothat it may be written upon with aqueous writing ink, and when used inlesser quantity imparts a lesser degree of water resistance, which,other things being equal, corresponds in general roughly to the quantityof sizing employed. Other sizes may be used, however, such as areemployed in the paper industry in place of rosin size, such for exampleasother saponifiable materials such as waxes, fatty acids and the like,either in saponified condition, or in emulsion in substantiallyunsaponified condition, as well as emulsions of various thermoplasticmaterials such as paraffin, all of which may be used in many cases inconjunction with rosin size. It is to be understood, however, that inrespect to the sizes mentioned, sizings containing paraffin or the likeare much more resistant to the action of alkaline filler than is rosinsizing mal or tub sizing, i. e. glue or materials used in place thereof,the purpose of which is to impart a stiffening or strengthening or thelike to the paper surface, and thus where I speak of sizing or sizedpaper in the claims I refer exclusively to the type of sizing describedin the previous sentences, and to the paper in which it is used.

In the practice of my invention if the size I use is to be precipitatedI may for example precipitate it in the heater, or may utilize theminimizing technique, (i. e. adding material to the mix under conditionsfavoring the minimizing of the time and/or intimacy of contact of theconstituents of the mix), in connection with the size precipitation orrestoration; or I may apply the size to, or precipitate it or restore itin, the web, or I may add previously precipitated sizing to the papermix or the web, or the like. In any and all of these cases thedeteriorating effect on the sizing of paper machine driers as ordinarilyoperated is lessened or substantially eliminated by the practice of myprocess.

The alkaline filler may be added to the mix in the beater, and/or underminimizing conditions, and/or to the web, as desired.

While I have'proposed above a theory which appears to explain the factssurrounding the present invention, it is to be distinctly understoodthat my invention is not limited in any way by this or any other theory,as regardless of theory, my invention is operable under the conditionsdisclosed.

Instead of using air as a heating medium, I

may employ other heated gas, preferably one which is non-inflammable andwhich may occur in industry in heated form, such as flue gas, preferablysuitably purified. Thus, where in the claims I use the words heated air,I mean to include any such suitable heated gas as an equivalent.

In some paper machines only one large steam drying cylinder is used inthe place ofthe usual bank of driers. Of course, my invention may be.suitably carried out on such a machine if desired,

and thus in the claims where I speak of drying paper on driers I mean toinclude the case where only one drier is used.

By the term alkaline filler, I mean substantially water insoluble fillerwhich when agitated in contact with freshly boiled distilled water, sayfor an hour, will impart a pH value to such water greater than 7.0, thatis, which will be on the alkaline side of the neutral point. Amongfillers included in this group may be mentioned calcium carbonate, ofwhich lime mud from the causticizing process is one form; calciumcarbonate magnesium basic carbonate employed in the paper disclosed inmy United States Patent No. 1,595,416, issued August 10, 1926; calciumcarbonate magnesium hydroxide disclosed in my United States Patent No.1,415,391, issued May 9,

1922; and other substantially water insoluble normal or basiccarbonates. of alkaline -earthf metals, (which expression is hereinintended to! include magnesium), or compounds, double salts, orphysically associated mixtures of these with one or more other acidsoluble materials of a substantially water insoluble nature.

By the term alkaline filler I also intend to include fibrous materialand/or other material such as paper coating constituents or the likecontaining one or more compounds of the character referred to, such asold papers or similar papers, broke, or the like.

The term drying when employed herein in connection with a paper web isused in its ordinarily accepted meaning in the art as referring to suchdrying as takes place subsequent to the passage of such web through thecustomary press sectionof the paper machine. 1

Where in the claims the expression major part of the drying is used, itmeans the removal by evaporation of more than half of the weight ofwater remaining in the web after the web has passed through thecustomary press section of the paper machine.

When I use the word paper herein, I use it in the broad sense to includeproducts of manufacture of all types and of all weights and thicknesses,which contain as an'essential constituent a considerable amount ofprepared fibre and which are capable of being produced on a Fourdrinier,cylinder, or other forming, felting, shaping or molding machine.

Of course it is to be understood that a combination of one or more ofthe three drying methods disclosed herein may be employedin drying thepaper instead of using only one of the methods alone.

By room temperature? as specifically used in the claims I mean theordinary temperature of the air in the paper machine room whichsurrounds the point of delivery of the wet web from the web-formingdevice and the customary press part of the paper machine.

Where in the claims,-I speak of the temperature of paper machine driers,I- refer to their surface temperature. 7 r

In certain of the claims Ihave stated that the paper may be dried "underconditions such that the temperature of the web is not raised above C.,by supplying heat to said web from a heat source above room temperature;in certain other of the claims I have stated that the drying isaccomplished by heating the paper web to an extent sufficient to elevatethetemperature thereof but insufficient to raise the temperature of theweb substantially in excess of 75 C."; and in certain other of theclaims I have stated that the drying operation is conducted byevaporating at least the major part of the water in the paper web byheating the web to an extent sufficient to elevate the temperaturethereof but insuificient to raise the temperature of the websubstantially in excess of 75 C., and thereafter heating the partiallydried web at a higher temperature. It is of course obvious that in thedrying of paper at atmospheric pressure in the ordinary manner on theusual steam heated paper machine driers, that, at the initial stage ofthe drying op eration, the web will not necessarily be raisedimmediately to a temperature higher than 75 C. However, as the webcontinues to contact with the steam heated drying surface, the web soonattains a temperature higher than 75 C. It will of course be understoodthat in the several expressions referred to above or in any other similar expression which may be used in.the claims,

I do not mean to include such condition which.

sure with ordinary steam heated paper machine driers.

While I have described in detail the preferred embodiments of myinvention, it is to be understood that the details of procedure,ingredients, methods of operation, apparatus, and arrangement of stepsmay be widely varied without departing from the spirit of the inventionor the scope of the subjoined claims.

I claim:

1. In a process of manufacturing paper filled with alkaline fillerwherein there is provided a water-containing paper web which containsalkaline filler comprising calcium carbonate and rosin sizing, andwherein heat from a heat source above room temperature is supplied tosaid watar-containing web to effect drying thereof, the improvementwhich comprises maintaining said web, from the time of formation thereofuntil at least the major part of the drying thereof has been efiected,at a temperature not exceeding 75 C. 1

2. A process according to claim 1 wherein said web is maintained at atemperature not exceeding 75 C. throughout substantially the entiredrying thereof.

3. A process according to claim 1 wherein said web containsthermoplastic material and wherein the temperature of the web which hasbeen subjected to drying until at least the major part of the water hasbeen evaporated is subsequently raised sufficiently to cause fluxing ofsaid thermoplastic material.

4. A process according to claim 1 wherein at least the major part of thedrying is effected by contacting the water-containing paper web withheated paper machine driers in a chamber under a vacuum such that theboiling point of water thereunder does not exceed a temperature of 7. Aprocess according to claim 1 wherein at least the major part of thedrying is effected by contacting the water-containing paper web withpaper machine driers heated to a temperature above 75 C. in a chamberunder a vacuum such that the boiling point of water thereunder does notexceed a temperature of 75 C.

8. A process according to claim lwherein at least the major part of thedrying is effected by contacting the water-containing paper web withpaper machine driers heated to a temperature above 75 C. in a chamberunder a vacuum such that the boiling point of water thereunder does notexceed a temperature of 65 C.

9. A process according to claim 1 wherein at least the major part of thedrying is effected by contacting the water-containing paper web withpaper machine driers heated to a temperature above 75 C. in a chamberunder a vacuum such that the boiling point of water thereunder does notexceed a temperature of 45 C.

' 10. A process according to claim 1 wherein at least the major part ofthe drying is effected on paper machine driers having a surfacetemperature above 75 C. but not substantially in direct contacttherewith. I

11. In the manufacture of paper filled with alkaline filler whereinthere is provided a watercontaining paper web containing alkaline fillercomprising calcium carbonate and rosin sizing and wherein thewater-containing web is subsequently dried, the improvement whichcomprises maintaining said water-containing web at a temperature notexceeding 75 C. from the time of the formation of said web up to thedrying thereof, and effecting the drying of said watercontaining web byheating the same to an extent sufficient to elevate the temperaturethereof but insuflicient to raise the temperature of the web above 75 C.

12. In the manufacture of paper filled with alkalineflller wherein thereis provided a watercontaining paper web containing alkaline fillercomprising calcium carbonate and rosin sizing and wherein thewater-containing web is subsequently dried, the improvement whichcomprises maintaining said water-containing web at a temperature notexceeding 75 C. from the time of formation of said web up to the dryingthereof, and subjecting said water-containingweb to a drying operationcomprising evaporating at least the major part of the water in saidwater-containing web by heating the same to an extent suflicient toelevate the temperature thereof but insuflicient to raise thetemperature of the web above 75 C., and thereafter heating the said webGERTIFIGATE OF CORRECTION. Patent No. 2,115,715. w 95 HAROLD ROBERTRAFTON.

It is hereby certified that error appeare in the printed specification 3of the above ninhhered patent requiring eorrection as follows; Page 5firet eolmnn, line 9, forv the wordlfinishes read. furnishes; and thatthe said Letters Patent should he read witlti this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this 19th day of July, A. D.- 1.958.

Henry Van'Arsdale, Acting Commissioner of Patents.

